In the preparation of bioabsorbable polymers, among the most widely studied lactones are ε-caprolactone, lactide and glycolide. Recent attention has been focused on improving the physical and biological properties of polymers and copolymers derived from these specific lactones.
Attempts to optimize the properties of copolymers of ε-caprolactone and glycolide are known, such as those proposed in U.S. Pat. Nos. 4,605,730 and 4,700,704. These patents propose single and two-stage polymerization processes for preparing the copolymers. Of particular interest is a two-stage polymerization process. Specifically, the aforementioned patents propose preparing a low molecular weight prepolymer of ε-caprolactone and glycolide, and then polymerizing in situ the resulting prepolymer with glycolide to produce a crystalline copolymer.
U.S. Pat. No. 5,133,739 proposes a crystalline copolymer comprising the reaction product of a predominant amount of a high molecular weight prepolymer of caprolactone and glycolide, and the balance glycolide. A surgical device such as a surgical filament, in particular a surgical suture, prepared by injection molding or melt spinning the crystalline copolymer is also proposed.
U.S. Pat. No. 7,148,315 proposes a monomer addition methodology to adjust monomer addition rates to a polymerization reactor for controlling bioabsorbable copolymer structure, improvement of monomer conversion, control of reaction temperature, and reduced reaction time. The technology is said to have utility in the copolymerization of monomers with different reactivity ratios, such as glycolide/lactide copolymers and glycolide/caprolactone copolymers. Monomer reactivity ratios and reaction kinetics are utilized to adjust monomer addition rates.
Certain aspects of the preparation of nonwoven constructs from synthetic, bioabsorbable polymers by melt blown extrusion are known. Unfortunately, the copolymers described in the aforementioned patents do not provide the most desirable properties when fabricated into nonwoven constructs. Significantly, when the copolymers are used to prepare nonwoven constructs, the copolymers cannot be melt blown or the resultant fiber diameter is undesirably large.
Therefore, it would be most desirable to prepare a copolymer of ε-caprolactone and glycolide which can be fabricated into useful nonwoven constructs. In particular, it would be desirable to prepare such a copolymer which can be melt blown into a nonwoven construct that exhibits outstanding physical and biological properties. Additionally, it would be desirable to prepare such a nonwoven construct of fine diameter. Such fine diameter construct may provide advantageous properties beyond mechanical and biological properties, such as diffusional properties important in drug release.